236 GENERAL SCIENCE 



Yeast is raised in large vats with mashed potatoes and hops at 

 a temperature of about 80 F. The yeast grows very rapidly. The 

 water is strained from the yeast by placing the yeast in cheese cloth, 

 after which it is mixed with starch to make it firm, and cut into 

 cakes to be sold as compressed yeast. Sometimes the yeast is dried 

 and sold as dried yeast cakes. 



In bread making, the dough is kept in a warm place for a time, 

 during which the yeast acts upon the small amount of sugar which 

 is found in all cereals. The housekeeper always places the dough in 

 a place where the temperature maintained will be such as to make 

 the yeast plants very active. They produce carbon dioxide and 

 alcohol from the sugar. This makes the bread rise, as the heat 

 expands the gas after the bread has been put into the oven. The 

 carbon dioxide and alcohol escape by diffusion. Bread raised by 

 the use of yeast contains no harmful ingredients such as are some- 

 times left by the use of baking powder. Bread left too long to 

 " rise " will sour, because the yeast plants change the alcohol into 

 an acid. During the process of cooking the bacteria are killed. 



QUESTIONS 



1. Why is carbon dioxide an essential factor in bread making? 



2. Why is it not possible to use any acid and a carbonate for 

 generating carbon dioxide in bread? 



3. Why are places cut in the dough on top of a loaf of bread? 



4. Why do some people prick the top of the bread with a fork? 



5. Why is alum baking powder objectionable? 



6. Why should we avoid the use of bread made with alum baking 

 powder? 



7. What is the best test for the presence of alum? Look up 

 others. 



8. Why is bread kneaded? 



9. Why are there sometimes large holes in certain parts of the 

 bread? 



10. What causes sour bread? 



11. What is salt rising bread? (Look this up). 



